1. Field of the Invention
The present invention relates generally to a transistor inverter, and is directed more particularly to a transistor inverter in which an undesirable radiation caused by the switching operation of the transistor is avoided.
2. Description of the Prior Art
With a prior art transistor inverter, a DC voltage is subjected to a switching operation to produce an envelope pulse signal. This pulse signal is increased or boosted in voltage by a transformer and then rectified to be a desired DC voltage. In this case, as the frequency of a switching signal is high, power consumption in the transistors is reduced. Therefore, the efficiency of the inverter is enhanced. However, since a relatively high frequency of a switching signal is produced at the secondary winding of the boosting transformer in this case, there appears a leakage to the outside through the electrostatic capacity formed between the primary and secondary windings of the transformer. This leakage of the signal represents an undesired radiation which will exert a bad effect on the other electronic instruments.
In the prior art, the transformer is shielded to avoid, to some extent, the occurrence of the undesired radiation therethrough.
In general, since the potential at the case of a transistor is selected equal to that at its collector electrode, it is ascertained that the switching signal at the primary winding of the transformer is leaked to the outside thereof through the case of the transistor.
Generally speaking, the case of the transistor is attached through an insulating layer made of, for example, mica and the like to a heat sink. This heat sink is attached directly to a metal chassis, so that it is also ascertained that since the switching signal is coupled in view point of AC through the electrostatic capacity between the case of the transistor and the heat sink (or chassis), the input power source acts as a kind of antenna.
The prior art, however, fails at present to show a method to avoid an undesired radiation caused by the electrostatic capacity between the case of the switching transistor and the chassis.